The main objective of the proposed research is to detemine if bronchiolitis, laryngotracheobronchitis (LTB) and acute upper respiratory tract infections (URI - common cold) in children cause prolonged abnormalities in pumonary function. The persistence of small airway abnormalities in asymptomatic children after acute respiratory illnesses and the possible relationship of such functional changes to chronic obstructive lung disease have not been defined. Children with bronchiolitis, LTB, and URI will be evaluated during the acute episode and at various intervals after the illness. Tests will include arterial gas tensions and appropriate - for - age pulmonary function tests (resistance, static or dynamic compliance, functional residual capacity, plethysmographic lung volumes, maximal expiratory flow volume curves on air and on a helium-oxygen mixture, determination of points of identical flow, maximum mid-expiratory flow rates, closing volumes, and the slope of phase 3 on the nitrogen-washout curves). Detailed viral studies and allergic evaluations will be done on all patients. An epidemiological study of the home environment in bronchiolitis will also be done. Children who had bronchiolitis or LTB 6-8 years previously will be recalled for detailed pulmonary function testing. All results will be compared to those obtained from a control group derived from the same population. The second aim of the project is to study further the nasal-airway and glottic-airway reflexes that may cause broncho- constriction and, thereby, some of the abnormalities in LTB, URI and asthma. A study of the benefits of racemic epinephrine and IPPB on the clinical course and blood gases in LTB is currently underway and will be extended. Asthmatic adolescents will be given aerosolized antigens (via the nasal route) while they hold their breath at total lung capacity. Following a prolonged expiration, maximal flow rates, resistance, and lung volumes will be measured and compared to pre-exposure values. The effects of atropine and topical nasal anesthetics on any changes in pulmonary function will be evaluated.